An uninterruptible power supply hereafter referred to as UPS, is used to provide backup power to critical loads in an electrical system. It is of utmost importance that the health of the batteries is known so that in the event of a utility line failure the batteries can support the load for the designated period of time. Conventional electronic battery test systems use two different approaches to test the batteries. The first approach simulates a failure of the utility line, transfers the load to the UPS, and measures the battery parameters. This approach risks the possibility that the load will not be supported when the test is initialized. A second approach utilizes additional contactors that switch load resistors across the batteries when a test is initialized. This approach adds cost, complexity, and the resistor loss becomes unmanageable for large systems. An electronic battery test system is disclosed that will illustrate a simple, low cost, method for testing the batteries under load without risking the capability to support the load at any time during the test. The system is comprised of a battery charger, batteries, and an inverter with a control system. The system is for use with a utility line, and load. This invention can be used in any system that contains a battery charger operated from an AC utility source that is directed in determining the health of a battery without compromising the back-up capability of the system.
Many applications require UPS systems to back up critical loads. There are different ways to ensure that the load will be supported in case of a utility line failure. Two common topologies used in the industry are the double conversion topology and the off line topology. The double conversion topology has a separate battery charger that operates from the AC line connected to the batteries and a separate output source that supplies the battery power to the loads. The output source could convert the battery to an AC output or a DC output. Off-line systems use the same inverter to either charge the batteries or support the load. When power from the utility line is present then it is passed to the load and the batteries are charged through the inverter. When the utility line fails the inverter switches from battery charging mode to inverting mode and the load is supplied by the batteries via the inverter.
Prior art methods have the following disadvantages with respect to battery testing. Some methods require batteries to be taken out of service, which risks that the load will not be supported in the event of an AC line failure. Other methods simulate a utility line failure and transfer to inverter to support the load; however, this poses a risk that the load is not supported if a battery has failed since the last test. Other methods of testing batteries require extra controllers, power switches to disconnect and reconnect the batteries, and a separate load that is large, costly, and inefficient for larger systems.
The present invention addresses the aforementioned limitations of the prior art by providing an apparatus and method that offers manual or programmable test features under micro-controller supervision that does not risk the load being dropped during the testing period. The battery test is performed by drawing a current from the battery and supplying that current into the utility grid. During the testing period battery parameters are monitored, tests results are saved, and alarms are generated based on historical data predicting battery degradation or weakness. The live circuit battery tester uses all common hardware with the battery charger and does not require additional disconnects or load banks.